Net hook fasteners

ABSTRACT

The present invention concerns a polymeric film hook netting comprising a continuous film backing having a net section formed of plurality of a first set of thermoplastic strands extending in a first direction and a second set of integral strands extending in a second direction at least one of which strands has upstanding hook elements and a second integral non-net film section.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 11/456,234, filed Jul.10, 2006, now allowed, the disclosure of which is incorporated byreference in its entirety herein.

FIELD OF THE INVENTION

The present invention concerns an extrusion formed reticulated web, meshor netting, which can be formed as reticulated hook fasteners for usewith hook and loopfasteners.

BACKGROUND OF THE INVENTION

Formation of net structures from a profile extruded film is disclosed inUS patent Applications 2004/0170802 and 2004/0170801 where a film isprovided with integral ribs. The film backing is cut at an angletransverse to the ribs forming a first set of strands for the netting.The second set of strands is formed from the coextruded ribs. Followingthe cutting step the film is elongated in the transverse direction tothe cut, generally along the length of the coextruded ribs opening thefilm up to create the netting. Hooks can be formed on the net strandsformed by this method by providing profiled ridges with hook profilesthat are also cut during the net formation process. This is a continuousmethod and creates a strong net hook structure. Incorporating this nethook into a fastening tab structure however is difficult.

SUMMARY OF THE INVENTION

The present invention is directed at a hook fastening tab net structureformed from polymer netting formed from an extruded film. The extrudedfilm netting has a first hook net section which is three dimensional,and has a first face and a second face and a second substantially planarsecond non-net section. The extruded film forming the netting isintermittently cut in regular intervals along a cut line dimension onone or more faces or alternatively in alternating fashion on the firstface and the second face in the three dimensional section, but notthrough at least a portion of a planar backing section that becomes thenon-net section. At least one face of the three dimensional section hasa plurality of profiled ridges or ribs that have the cross-sectionalprofile of a hook head, and extend at least partially transverse to thecut line dimension. The cut film is then stretched (oriented) at leastpartially transverse to the cut line dimension creating a hook nettingcharacterized by net strands extending in the cut line dimension whichstrands have a width preferably substantially equal to the hook headwidth, and an integral non-net section. By “integral”, as defined forthis invention, it is meant that the net section and non-net sections orthe various strands are contiguous, boundaryless structures formed fromthe same polymer film backing, i.e. without seams, bonding or the like.Integral would not mean side-by-side connected materials, laminates oftwo or more materials or the like. The polymer netting is preferablymade by a novel adaptation of a known method of making hook fasteners asdescribed, for example, in U.S. Pat. Nos. 3,266,113; 3,557,413;4,001,366; 4,056,593; 4,189,809 and 4,894,060 or alternatively6,209,177, the substance of which are incorporated by reference in theirentirety.

The preferred method generally includes extruding a thermoplastic resinthrough a die plate, which die plate is shaped to form a nonplanar orthree dimensional film section which could be either a backing with aregularly oscillating peak and valley base structure that oscillatesfrom a top surface to a bottom surface forming longitudinally extendingridges using both faces of the film, or a substantially planer base withridges or ribs extending from at least one and generally both faces ofthe base, and a second substantially planar backing section. This planarsection could also have ridges or ribs on one or both faces but willhave a substantially planar backing that would not be cut in thesubsequent cutting step forming the net section from the threedimensional section. The hook netting section is formed by transverselycutting through the film three dimensional film section in the thicknessdimension (Z dimension) at spaced intervals along a length (Xdimension), at a transverse angle, to form discrete cut portions. Thecuts can be on one or both faces of the three dimensional film and areat least through the ridges having a hook head profile. Subsequently,longitudinal stretching of the film (in the direction of the ridges orthe X dimension or direction) separates these cut portions of the threedimensional film backing, which cut portions then form one set ofstrands or legs of the hook netting, namely the transverse extendingstrands or legs (Y dimension) of the hook netting. The ridges, orcontinuous uncut regions of an oscillating backing, between the cutlines on an uncut face create lands or strands, and these uncut portionsof the ridges or backing form the lengthwise strands (X dimension) ofthe hook netting section.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described with reference to theaccompanying drawings wherein like reference numerals refer to likeparts in the several views, and wherein:

FIG. 1 is a schematic view of a method of forming the invention netting.

FIG. 2 is a cross-sectional view of a die plate used to form a precursorfilm used in accordance with the present invention.

FIG. 3 is a cross-sectional view of a die plate used to form a precursorfilm used in accordance with the present invention.

FIG. 4 is a perspective view of a first embodiment precursor film inaccordance with the present invention.

FIG. 5 is a perspective view of the FIG. 4 film cut on one face atregular intervals.

FIG. 6 is a perspective view of a netting in accordance with the presentinvention having hook elements.

FIG. 7 is a perspective view of another embodiment precursor film inaccordance with the present invention.

FIG. 8 is a perspective view of the FIG. 7 film cut on one face atregular intervals.

FIG. 9 is a perspective view of a netting in accordance with the presentinvention produced from the FIG. 8 cut film.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

A method for forming a hook netting of the invention is schematicallyillustrated in FIG. 1. Generally, the method includes first extruding aprofiled film section through a die plate 1, shown in FIGS. 2 and 3. Thethermoplastic resin is delivered from an extruder 51 through the die 52having die plate with a cut opening 2 having a nonplanar (i.e. threedimensional) section 33 and a substantially planar section 34 or 34′.The die opening can be cut, for example, by electron dischargemachining, shaped to form film 10 with a three dimensional section 33,as shown in FIGS. 4 and 7, which would also have elongate spaced hookhead shaped structures 7, 7′ extending along one or both surfaces 3 and4 of the films 10. The elongate hook head structures 7, 7′ provided onone or both surfaces 3 and 4 of the film 10, can have any predeterminedhook like shape, including t-shaped, j-shaped, y-shaped or like. Thefilm 10 generally is pulled around rollers 55 through a quench tank 56filled with a cooling liquid (e.g., water), after which the film 10three dimensional section 33 is transversely slit or cut at spacedlocations 8 along its lengths, by a cutter 58 to form discrete cutportions of the film 10 three dimensional section 33. The film 10 is notcut, or at least is not cut through the entire film, in thesubstantially planar backing sections 34. As shown in FIGS. 5 and 8, thedistance 21 between the cut lines 20 corresponds to about the desiredwidth 21′ of the cut portions 31 to be formed, as is shown, for example,in FIGS. 6 and 9. The cuts 20 can be at any desired angle, generallyfrom 30° to 90°, with respect to the lengthwise extension of the film(X-direction). Optionally, the film 10 can be stretched prior to cuttingto provide further molecular orientation to the polymeric film 10,reducing the thickness of the film 10 and any structures on the film.The cutter can cut using any conventional means such as reciprocating orrotating blades, lasers, or water jets, however preferably the cutteruses blades oriented at an angle of about 60 to 90 degrees with respectto lengthwise extension (X direction) of the film 10.

The film 10, as shown in FIGS. 4 and 7, has a first top face 4 and asecond bottom face 3 with a film thickness 14 of from 25 microns to 1000microns, preferably 50 microns to 500 microns. The film 10 is threedimensional in section 33 where either the film base oscillates, such asby peaks (17, 45) and valleys forming substantially continuous ridges ata first upper plane 12 and a second lower plane 13 (as shown in FIGS.1-6), and/or has discrete ridges (22,23,7) which are formed on acontinuous film base or backing layer.

In the embodiment of FIGS. 1-6 by oscillating, it is meant the filmitself or the continuous film backing, not just structures on the filmsurface, is three dimensional or nonplanar and oscillates from an upperplane 12 to a lower plane 13. The film backing oscillates around amidline 15 and the three dimensional film is characterized by a firsthalf 6 extending on one side of the midline 15 and a second 5 halfextending on the opposing side of the midline 15. The peaks (17, 45) ofthe ridges on the three dimensional nonplanar film backing, or the topface of the film backing, generally extends at least to the upper plane12. The peaks of ridges or the film backing, or individual peaks canterminate below or above the upper plane 12 preferably at a pointbetween the midline 15 and the top plane 12. The peaks 17 on the bottomface 3 of the film backing also extend generally at least to the lowerplane 13. However, again the film backing plane or individual peaks canterminate above or below the lower plane 13 and preferably between themidline 15 and the lower plane 13. The peaks generally alternate fromthe lower plane 13 to the upper plane 12 but multiple peaks can extend,in a row, to either the upper plane or the lower plane without extendingto the other half of the nonplanar film face by having the intermediatepeaks only extending to the midline, or below the midline, on the sameside of the midline. Generally, an oscillating nonplanar film will haveat least about 2 peaks (45 and/or 17) per linear centimeter (cm) andpreferably at least 5 peaks per centimeter extending up to 50 peaks perlinear centimeter. Each peak preferably will extend past the midline ofthe film to an extent such that the underside 18 of the peak extendspast the underside of 19 of the adjacent opposing peak by at least 10microns, preferably at least 50 microns. The distance 6 or 5 between themidline and the upper plane 12 or lower plane 13 is generally about 50microns to 1000 microns preferably about 100 microns to 500 microns.

The film of the embodiment of FIGS. 1-4 is then cut on either the upperface 4 or the lower face 3 from the upper plane 12 toward the midline 15or from the lower plane 13 toward the midline 15, as shown, for example,in FIG. 5 in the three dimensional section 33. The cuts 20 extend fromthe upper or lower plane at least through the undersides 18 or 19 of thepeaks 17 or 45. At least some of the peaks 17 or 45 on a face are cutand preferably all or substantially all of the peaks are cut, howeverwithout cutting through the integral planar backing section 34. The cuts20 will preferably at least extend to the midline of a film backing.Generally the cuts can extend so that they terminate prior to theundersides (18 or 19) of the opposing peaks. Preferably, the cuts willterminate before reaching substantially all of the undersides (18 or 19)of the opposing peaks to avoid severing the film. Undersides (18 or 19)of the peaks on one face will form the valleys of the opposing face. Inan alternative embodiment, the film peaks (17 or 45) can be cut on bothfaces as described above as long as the cuts on opposing faces areoffset so as not to completely sever the film and these cuts do not cutthrough the planar backing section 34 as shown in FIGS. 5 and 6, leavingthis section without holes or perforations. The distance 21 between cuts20, which forms the cut portions 31, is generally 100 microns to 1000microns, preferably from 200 microns to 500 microns. The cut portions 31form the strands 44 extending in the cross-direction of the net section40. The strands 41 extending in the lengthwise direction are formed bythe uncut portions of the nonplanar film section. These lengthwisestrands 41 are generally continuous when the film backing is cut on onlyone face. At least some of the cross direction strands 46 are at leastin part generally always continuous when the cuts are continuous. Thehook elements 48 are formed by the cut hook shaped ridge 7 forming thepeak 45 on the upper face 4 of the three dimensional film section 33.

After cutting of the film 10 the film is longitudinally stretched at astretch ratio of at least 2:1 to 4:1, and preferably at a stretch ratioof at least about 3:1, preferably between a first pair of nip rollers 60and 61 and a second pair of nip rollers 62 and 63 driven at differentsurface speeds preferably in the lengthwise direction. This forms theopen three dimensional netting shown in, e.g., FIGS. 6 and 9. Roller 61is typically heated to heat the film prior to stretching, and roller 62is typically chilled to stabilize the stretched film. Optionally, thefilm can also be transversely stretched to provide orientation to thefilm in the cross direction and flatten the profile of the nettingformed. The films 10 could also be stretched in other directions or inmultiple directions. The above stretching method would apply to allembodiments of the invention. When the films are cut on only one face,the open areas 43, 43′ generally are separated by linear strands 41, 41′which strands have a non-rectilinear cross-section or are nonplanaralong their length or both. The transverse strands 44, 44′ can be planaror nonplanar and they can be rectilinear in cross-section. Nonplanarstrands or a nonplanar netting section provides for a more flexiblenetting which creates breathability both through the film (by the openarea of the netting) and along the plane of the reticulated netting, dueto its nonplanar nature. The open areas 43, 43′ generally comprise aboutat least 50 percent of the surface area of the netting, excluding thenon-net section, and preferably at least 60 percent. The surface area ofthe netting is the planar cross-sectional area of the netting in the X-Yplane. This large percentage open area creates an extremely flexible andbreathable netting. The hook heads formed on hook nettings arepreferably smaller than the individual openings in the netting in thedirection parallel with the hook head overhangs such that the hooknetting is non-self engaging.

Stretching causes spaces 43, 43′ between the cut portions 31 of the filmand creates the longitudinal strands 41, 41′ by orientation of the uncutportions of the film. In the embodiment of FIGS. 1-6 the transversestrands 44 are formed by interconnected cut film backing portions eachof which has leg portions which join at the peak 45. In the embodimentof FIGS. 7-9 the transverse strands 44′ are formed solely by the cutfilm backing. In the embodiment of FIGS. 1-6 the leg portions ofadjacent cut portions are connected by the lengthwise strands (e.g., 41)or the uncut film portions.

FIG. 6 is an exemplary polymeric netting, which can be produced,according to the first embodiment of the present invention, generallydesignated by the reference numerals 40. The cut ridges 7 on the uppersurface 45 form a multiplicity of hook members 48 and the uncut planarbacking section forms a non-net section 34 which can be used as anattachment surface, a finger-lift or like.

The second embodiment of FIGS. 7-9 is like the first embodiment in thatthe film 10 is cut on the upper 4 and/or lower 3 face at least on a faceprovided with a hook shaped 7′ ridge 22 and an opposing ridge 23. Thecuts 20 extend from the top of the hook shaped 7′ ridge 22 to at leastthe starting point 25 of the opposing ridge 23 through the film backing26. The film backing 26 is not in the planar backing section 34, whichcan be accomplished by lowering section 34 or raising three-dimensionalsection 33 relative to the cutting blades. The cuts can extend into theopposing ridges 23 but must terminate before severing these ridges 23. Asecond cut could also be done on the opposing face 3 cutting into ridges23, which may also be provided with hook shaped profiles, as long asridges 23, and the planar backing section 34, are not cut all the waythrough or severed.

The netting is formed having transversely extending strands 44, 44′ thatare created by the cut portions of the three-dimensional sectionextending in the cross direction and longitudinally extending strands41, 41′ created at least in part by uncut portions of the film 10 oropposing ridges 23. When tension or stretching is applied to the film 10in the lengthwise direction, the cut portions 31 of the film separate,as shown in the embodiments of FIGS. 6 and 9. When the film 10 is cut ononly one face, the uncut portions of the film or strands, between cutlines, are aligned in the lengthwise direction resulting in formation oflinear strands 41, 41′ extending in the lengthwise direction uponstretching or tensioning of the cut film. The transverse strands 44, 44′are created by the cut portions 31 or the backing in the embodimentsshown in FIGS. 6 and 9. The cut portions 31 connect the longitudinalstrands 41, 41′ formed by the uncut portions of the opposing strands 23or the backing.

The invention netting is characterized by having no bond points orbonding material at the cross-over points of the transverse andlongitudinal strands or between the net section 33′ and the non-netsection 34′ as they are all formed of one integral film backing. The netand non-net sections (33′ and 34′) are integrally formed of a continuousthermoplastic material. The connection between the strand elements andthe non-net section 34′ is created in the film formation process wherethe strands are created by cutting of an integral film. As such the netat the strand cross-over points and the net non-net boundary is acontinuous homogeneous polymeric phase. Namely, there are no interfacialboundaries caused by fusion or bonding of separate strand elements atthe strand cross-over points or between the two sections.

Preferably, at least one set of strands and the non-net section hasmolecular orientation caused by stretching; this generally would be thelongitudinal strands. These oriented strands could be of anycross-sectional profile and would tend to become rounded due to polymerflow during stretching. Orientation creates strength in these strandsproviding a dimensionally stable web in the direction of orientationwith continuous linear strands. Unoriented strands are generallyrectilinear in cross-section due to the cutting operation. In theembodiment of FIG. 6 the two sets of strands generally will intersect aplanar face of the netting at an angle α, in the Z or thicknessdirection, of greater than zero (0) generally 20 degrees to 70 degrees,preferably 30 degrees to 60 degrees.

Suitable polymeric materials from which the netting of the invention canbe made include thermoplastic resins comprising polyolefins, e.g.polypropylene and polyethylene, polyvinyl chloride, polystyrene, nylons,polyester such as polyethylene terephthalate and the like and copolymersand blends thereof. Preferably the resin is a polypropylene,polyethylene, polypropylene-polyethylene copolymer or blends thereof.

The netting can also be a multilayer construction such as disclosed inU.S. Pat. Nos. 5,501,675; 5,462,708; 5,354,597 and 5,344,691, thesubstance of which are substantially incorporated herein by reference.These references teach various forms of multilayer or coextrudedelastomeric laminates, with at least one elastic layer and either one ortwo relatively inelastic layers. A multilayer netting could also beformed of two or more elastic layers or two or more inelastic layers, orany combination thereof, utilizing these known multilayer coextrusiontechniques.

Inelastic layers are preferably formed of semicrystalline or amorphouspolymers or blends. Inelastic layers can be polyolefinic, formedpredominately of polymers such as polyethylene, polypropylene,polybutylene, or polyethylene-polypropylene copolymer.

Elastomeric materials which can be extruded into film include ABA blockcopolymers, polyurethanes, polyolefin elastomers, polyurethaneelastomers, EPDM elastomers, metallocene polyolefin elastomers,polyamide elastomers, ethylene vinyl acetate elastomers, polyesterelastomers, or the like. An ABA block copolymer elastomer generally isone where the A blocks are polyvinyl arene, preferably polystyrene, andthe B blocks are conjugated dienes specifically lower alkylene diene.The A block is generally formed predominately of monoalkylene arenes,preferably styrenic moieties and most preferably styrene, having a blockmolecular weight distribution between 4,000 and 50,000. The B block(s)is generally formed predominately of conjugated dienes, and has anaverage molecular weight of from between about 5,000 to 500,000, which Bblock(s) monomers can be further hydrogenated or functionalized. The Aand B blocks are conventionally configured in linear, radial or starconfiguration, among others, where the block copolymer contains at leastone A block and one B block, but preferably contains multiple A and/or Bblocks, which blocks may be the same or different. A typical blockcopolymer of this type is a linear ABA block copolymer where the Ablocks may be the same or different, or multi-block (block copolymershaving more than three blocks) copolymers having predominately Aterminal blocks. These multi-block copolymers can also contain a certainproportion of AB diblock copolymer. AB diblock copolymer tends to form amore tacky elastomeric film layer. Other elastomers can be blended witha block copolymer elastomer(s) provided that they do not adverselyaffect the elastomeric properties of the elastic film material. A blockscan also be formed from alphamethyl styrene, t-butyl styrene and otherpredominately alkylated styrenes, as well as mixtures and copolymersthereof. The B block can generally be formed from isoprene,1,3-butadiene or ethylene-butylene monomers, however, preferably isisoprene or 1,3-butadiene.

With all multilayer embodiments, layers could be used to providespecific functional properties in one or both directions of the nettingor hook netting such as elasticity, softness, stiffness, bendability,roughness or the like. The layers can be directed at different locationsin the Z direction and form hook element cut portions or uncut portionsthat are formed of different materials. For example, if a cut portion iselastic, this results in a net which is elastic in at least thetransverse or cut direction. If the uncut portions are elastic thiswould result in a netting that may be closed but is elastic in thelongitudinal direction.

The hook elements formed on the cut portions form a reticulated nettinghaving hook engaging elements providing a breathable, compliant anddeformable hook netting. A hook netting of this type is extremelydesirable for limited use articles such as disposable absorbent articles(e.g., diapers, feminine hygiene articles, limited use garments and thelike), particularly with the uncut nonplanar non-net section 54 formingan attachment surface. In this case the net portion would form afastening portion of a fastening tab and have a size appropriate forthis end use. The non net section would function as an attachmentsurface to attach to the absorbent garment and could be joined to theabsorbent article such as by sonic bonding, an adhesive (which could bea pressure sensitive adhesive “PSA” coating on the non-net area). Thenet area could be further reinforced by attachment to a nonwovenmaterial, which would maintain its flexibility and breathability whileadding further strength and softness. A preferred method would be byhydroentangling a nonwoven with the net hook section.

Example 1

A hook net material containing both net and non-net areas was made usingapparatus similar to that shown in FIG. 1. A polypropylene/polyethyleneimpact copolymer (SRC7-644, 1.5 MFI, Dow Chemical) was extruded with a6.35 cm single screw extruder (24:1 L/D) using a barrel temperatureprofile of 177° C.-232° C.-246° C. and a die temperature ofapproximately 235° C. The extrudate was extruded vertically downwardthrough a die having an opening cut by electron discharge machining toproduce an extruded profiled web (henceforth referred to as theprecursor film). After being shaped by the die, the extrudate wasquenched in a water tank at a speed of 6.1 meter/min with the waterbeing maintained at approximately 10° C. The precursor film wascomprised of a planar backing base layer with elongated spaced ribsprojecting from both surfaces of the base layer. The precursor film wassimilar to that shown in FIG. 7 except that the lower ribs were the sameshape as the upper ribs and they were offset between the upper ribs.Also, the film contained ribs over its entire width rather than havingthe flat planar backing section 34 shown in FIG. 7.

The precursor film (approximately 13 cm width) was then advanced througha cutting station possessing a vacuum shoe that ordinarily serves tokeep the film flat. However, a 100 micron thick, 5 cm wide piece ofsilicone tape had been placed on the surface of the cutter shoe. Thisserved to elevate the center 5 cm of the precursor film such that thecutting blades would cut deeper into the web in this area than it wouldin the areas that were in direct contact with the vacuum shoe. In thismanner, the elevated precursor film (the three dimensional section) waspassed through the cutting station such that the upper ribs and the baselayer (but not the lower ribs) were transversely cut at an angle of 23degrees measured from the transverse direction of the film, over thecenter 5 cm of the film which had been elevated by the silicone tape. Inthe surrounding areas of the film, where the film was not elevated bythe silicone tape, the upper ribs only (i.e. not the base layer or lowerribs) were cut at the same 23 degree angle. The spacing of all cuts was305 microns. After cutting the ribs, the base of the precursor film waslongitudinally stretched at a stretch ratio of approximately 3.65 to 1between a first pair of nip rolls and a second pair of nip rolls tofurther separate the individual hook elements to approximately 8.5hooks/cm. There were approximately 15 rows of ribs or cut hooks percentimeter. The upper roll of the first pair of nip rolls was heated to143 C to soften the web prior to stretching.

Where the base layer had been cut, the stretching served to generateopenings so as to produce a hook net section similar to that shown inFIG. 9 (with the same differences noted as in FIG. 7). Where the baselayer had not been cut, a non-net hook material (i.e. hook elements on acontinuous, nonapertured backing) was produced. In this manner, a hooknet was produced containing both net and non-net areas, with no bondpoints or bonding material between the net and non-net sections.

1. A method for forming a thermoplastic polymeric netting comprisingextruding a film comprising a first three dimensional polymer filmsection having a series of ridges extending as peaks and valleys from atop surface to a bottom surface, which peaks and valleys extend in afirst direction forming continuous ridges, and simultaneously extrudinga second substantially continuous planar backing section having asubstantially planar backing, cutting said three dimensional filmsection on at least one face in a second direction at an angle to saidfirst direction at multiple cut lines substantially through the film soas to form a plurality of cut portions without cutting through thebacking of the second substantially planar backing section, orientingsaid cut film in said first direction so as to separate said cutportions forming a net section with a set of separated strands connectedby uncut portions and a non net section formed by the uncut backing ofthe planar backing section.
 2. The method of claim 1 wherein the threedimensional film section has at least one ridge formed into a hookshaped profile that is cut by the multiple cut lines forming a net hooksection.
 3. The method of claim 1 wherein the film has a thickness offrom 25 to 1000 microns.
 4. The method of claim 3 wherein the film has athickness of from 50 to 500 microns.
 5. The method of claim 1 whereinthe peaks are formed by discrete ridge structures on opposite faces of acontinuous film backing.
 6. The method of claim 1 wherein the peaks areformed by an oscillating film backing.
 7. The method of claim 5 whereinat least some of the peak forming ridges have hook shaped structures. 8.The method of claim 1 wherein there are at least 2 peaks per linear cmof the film.
 9. The method of claim 1 wherein there are at least 5 to 50peaks per linear cm of the film.
 10. The method of claim 4 wherein atleast some of the peak forming ridges have hook shaped structures.